This invention relates generally to game balls, and more particularly to a game ball, such as a golf ball, having an ionomeric cover.
Before the development of ionomers, balata was the preferred material for golf ball covers. Polyethylene also was proposed for use as a golf ball cover material but was generally deemed highly inferior to balata in imparting playability and durability characteristics to the ball due to its brittleness and high hardness, and thus never became a commercially successful golf ball cover material.
Balata golf ball covers have now been replaced to a great extent by ionomeric cover materials. Ionomers are copolymers of an olefin and an .alpha., .beta.-ethylenically unsaturated carboxylic acid with a portion of the carboxylic acid groups neutralized by a metal ion. The metal ions serve as crosslinking agents, as they are ionically bonded to carboxylic acid groups in adjacent copolymer chains. Instead of having thermally irreversible covalent bonding, ionomers have thermolabile crosslinking in which metal ions become part of the chemical structure of the ionomer upon crosslinking, and these crosslinks are reversible. For purposes of this application, this type of crosslinking is referred to as ionic crosslinking. One of the advantages of ionic crosslinking in golf ball materials is the ability of ionic bonds to re-form after breaking as a result of processing at elevated temperatures.
There are numerous advantages to the use of ionomers in making golf ball covers. On the other hand, one drawback of conventional golf balls with soft ionomeric covers are that the covers are prone to scuffing and cutting, particularly when hit with irons which have sharp grooves. It would be useful to develop a golf ball with a soft ionomeric cover which is highly resistant to cutting and scuffing by sharp-grooved clubs. Furthermore, it would be useful to improve the heat resistance of soft ionomeric golf ball covers without hardening the covers.